1. Field of the Invention
The present invention is related to an electric machine including a stator, a rotating shaft with a rigidly fixed rotor attached to it, and a frame in which the stator is secured. The frame has an end shield on each side in which one rolling bearing each is secured through which the shaft having a shaft stub is mounted, which protrudes beyond the operating-side bearing. The shaft has a central longitudinally extending bore in which a tube is centrally secured. A device, secured on the end shield at the end of the shaft at the operating-side bearing outside the machine frame, is provided through which a cooling liquid, preferably water, enters the tube and flows back via the space between tube and the bore.
2. Discussion of Background and Material Information
In electric motors waste heat is generated that must be dissipated. Dissipation can be accomplished through fresh air cooling with regard to which a differentiation is made between natural cooling through moving air or radiation without the aid of a fan, induced ventilation through a fan mounted on the rotor or driven by it, and forced-air cooling directly through forced air. The effect of natural cooling and induced ventilation depends upon the speed of rotation of the machine, while forced-air cooling does not depend on the rotation of the machine. In addition, direct water cooling through water flowing in tubes in the frame is also possible, which is also independent of the speed of rotation. Another kind of cooling is circulatory cooling in which the cooling medium, e. g., air, hydrogen, or something similar, flows in circulation through the machine and a water or air cooler. Circulatory cooling can be designed to be dependent on the rotation speed or independent of it.
In United Kingdom Patent Publication No. GB-A-1 019 804 the cooling of the rotor shaft in a high-speed electric machine is described. Here the shaft has a through bore in which a tube is centrally secured. A special part with radial bores to secure the tube in the through bore and to seal off the tube and the through bore on one side is necessary. This part requires a high degree of processing because of the bores. Further, the sealing of this part in the bore when liquid coolant is used is certainly problematic.
In the rotor shaft cooling systems disclosed in International Patent Publication No. WO-A-90/09053 and in French Patent Publication No. FR-A-1 163 764 the shaft also has a through bore that is closed on one side with a part.